Method of making rimmed steel



United States Patent Ice 3,414,041 METHOD OF MAKING RIMMED STEEL John Gilbert Cutton, Youngstown, Ohio, assignor to United States Steel Corporation, a corporation of Delaware No Drawing. Filed May 10, 1966, Ser. No. 548,865 4 Claims. (Cl. 164-56) ABSTRACT OF THE DISCLOSURE A method of making a rimmed ingot having higher carbon content in the core than the rim by teeming an ingot of low-carbon steel, adding rimming agents during teeming, permitting rimming to proceed for a short time after filling the mold, then adding carburizing material to the mold to give the core a carbon content about twice that of the rim.

This invention relates to rimmed steel. More particularly, the invention relates to a method of making rimmed steel having a low carbon rim for good surface properties and a high carbon core for increased strength. The invention also relates to a rimmed steel ingot having at least about 0.2% carbon in the core and a unique core and rim carbon relationship.

The various types of steel ingots-killed, semi-killed, capped and rimmedare dependent for their metallurgical characteristics upon the extent to which gas evolution is permitted to occur. Control of gas evolution is accomplished by controlling the amount of oxygen dissolved in the liquid steel and thereby influence the degree to which the reaction between carbon and oxygen will occur. As gas evolves from a teemed ingot, due to the introduction of deoxidizing agents to the steel, the ingot experiences a boiling action which is referred to as rimming. For rimmed steels, proper rimming action in the core is necessary to produce the surface conditions and ingot structure desired.

Generally, rimmed steel is tapped without deoxidizing additions to the steel in the furnace and with only small additions in the ladle, in order to maintain sufficient oxygen present to give the desired gas evolution when reacting in the mold with carbon. When the metal of the ingot mold begins to solidify, there is a surge of gas at the edge of the ingot resulting in an outer rim of relatively clean metal. The thickness of the outer skin depends on the control and the effectiveness of the rimming action.

The strength and other physical properties of products made from rimmed steel ingots depends to a large extent upon the carbon content of the steel composition. In conventional rimmed steel, the carbon content of the rim is lower than the carbon content of the core. However, the maximum carbon content which can be obtained in the core of rimmed steels made from heats of low carbon steels, i.e. steels containing less than about 0.15% carbon, is under 0.16%. For many applications such steels would not possess satisfactory physical properties. On the other hand, it is desirable to maintain a low carbon rim to provide maximum surface ductility and formability.

The present invention provides a novel rimmed steel ingot, and a method of making same, whichpossesses a satisfactory low carbon rim for good surface properties but which has a relatively high carbon core for increased strength. According to the invention there is provided a method of making rimmed steel with at least 0.2% carbon in the core from a heat of low carbon steel which comprises providing a heat of low carbon steel, teeming the steel into a mold, adding rimming agents during teeming and, after filling the mold, adding sufiicient carburizing 3,414,041 Patented Dec. 3, 1968 material to the steel in the mold to produce a rimmed steel ingot with a carbon content of at least 0.2% carbon and a rim and carbon relationship such that the carbon content of the core is at least about twice the carbon content of the rim. The carburizing agent is desirably added to the steel after it has rimmed for at least 30 seconds, preferably 30 to seconds. The carburizing agent is preferably a pulverant material such as ground coke, although any suitable carburizing agent may be employed.

The following examples will aid in the understanding of the invention. A heat of low carbon steel containing 0.12% carbon, 0.35% manganese, 0.007% phosphorus, 0.021% sulfur, was prepared. This heat was teemed into five ingot molds, four of which were treated in accordance with the invention. Ingots 1 and 2 were cast in a 21 x 23 inch mold. Sixten ounces of sodium fluoride and two ounces of aluminum were added near the bottom. A fairly good rimming action was observed which began immediately. After the rimming action proceeded for about 1 minute, 13 /2 pounds of pulverant carbonaceous material was added to the rimming ingot. After initially surging, the ingot rimmed satisfactorily.

Ingots 3 and 4 were cast in a 24 x 29 inch mold and were also inoculated with sixteen ounces of sodium fluoride and two ounces of aluminum which were added near the bottom. The rimming action was the same as for ingots 1 and 2, and after about 1 minute, 15 /2 pounds of the same carburizing agent was added to the rimming ingot.

For comparison, the 5th ingot was cast and inoculated with sixteen ounces of sodium fluoride and two ounces of aluminum in the same manner as ingots 1 through 4, but no carburizing agent was added. After solidification, samples were removed from each of the five ingots to determine the carbon content of both the rim and the core of each ingot. These results are tabulated below.

TABLE I Ingot Percent carbon-rim Percent carbon-core As can be seen, the carbon contents in the core of each of the rimmed steel ingots produced in accordance with the invention was considerably higher than the carbon content of the core of ingot No. 5. The physical properties of products made from ingots produced according to the invention are superior to the products produced from conventionally-made rimmed steel ingots having considerably lower core-carbon contents.

Rimmed steel ingots having cores with a high carbon content are useful in applications Which require good surface properties and which must possess good formability but which require relatively high strength (for low carbon rimmed steels). Brake-shoe linings are a typical example of a use to which rimmed steel made in accordance with the invention may be put.

It is apparent from the above that various changes and modifications may be made without departing from the invention. Accordingly, the scope of the invention should be limited only by the appended claims.

I claim:

1. A method of making rimmed steel with at least 0.2% carbon in the core which comprises providing a heat of low carbon steel, teeming said steel into a mold, adding rimming agents during said teeming and, after filling said mold, adding sufficient carburizing material to the steel in said mold to produce a rimmed steel ingot with a core-carbon content of at least 0.2% carbon and a core and rim carbon relationship such that the carbon content of the core is at least about twice the carbon content of the rim.

2. A method according to claim 1 wherein the carburizing material is pulverant carburizing agent.

3. A method according to claim 2 wherein the carburizing agent is added to the steel in the mold after the steel has rimmed for at least about 30 seconds.

4. A method according to claim 3 wherein said carburizing agent is added after the steel has rimmed for between 30 and 90 seconds.

References Cited UNITED STATES PATENTS Cole 164-55 Hachiya et al 16456 Easton "75-58 X Hamilton 16456 Poole 16455 X Brown et a1. 164-57 Hale 16456 I. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

